HELP! Mcculloch 1635 fuel tank venting

[FJMILLER]

Hi there, I'm new here and this is only my second post....did a search with no luck

I'm having issues getting my MAC 1635 to run smoothly and when I shut it off I can hear noise from the gas cap. Unscrew the cap and you get a whoosh of air rushing into the tank.....so my question is...
How are these tanks supposed to be vented? The cap does not appear to have any sort of vent in it.

 

[heimannm]

There is supposed to be a duckbill valve in the fuel tank. You have to remove the 1/2 wrap handle, open the housing, and remove the fuel tank to access it as it is on the bar/clutch side of the fuel tank.

Mark